Structural panel and method of making same

ABSTRACT

A structural panel for use in building construction and the like wherein side skin sheets of fiber-reinforced polyester are spaced to form a mold cavity to receive a foamable resin composition which, upon curing, is integrally secured to the skin sheets so as to prevent delamination of the skin sheets from the core. The methods of making the side skin sheets and introducing the foamable core composition therebetween provide a structural panel of high strength and durability independent of the size of the panel, with increased core integrity over panels heretofore available.

United States Patent 1191 Elmore et al.

1111 1451 Nov 5, 1974 [54] STRUCTURAL PANEL AND METHOD OF 3,511,7385/1970 McGuire 264/45 X MAKING SAME 3,551,947 1/1971 Jennings 264/453,560,285 2/1971 Schroter et a1. 264/45 X 1 Inventors: Rlchard e; BenJ mM- 3,637,459 1/1972 Parish etal. 161/161 Couch, both Of Herrm, 111. 3,711,581 1/1973 Fowler et a1 264/45 X [73] Asslgnee: glura-PlexIndustr1es,'Inc., Peoria, Primary Examiner H S Cockeram r 1 Attorngy 4 ge r t, o r FirmJohnson, Dienner, Emrich, [22] Filed: Jan. 17, 1972Verbeck & Wagner 1 [21] Appl. No.: 218,398

- [57] ABSTRACT A structural panel for use in building construction and[52] Cl 3? the like wherein side skin sheets of fiber-reinforced 51] IntCl 27/0'0 polyester are spaced to form a mold cavity to receive [58]Fie'ld 161/161 a foamable resin composition which, upon curing; is264/45 integrally secured to the skin sheets so as to preventdelamination of the skin sheets from the core. The [56] References Citedmethods of making the side skin sheets and introducing the foamable corecomposition therebetween pro- UNITED STATES PATENTS vide a structuralpanel of high strength and durability 2,827,665 3/1958 Rogers et a1264/54 independent ofthe size of the panel, with increased graham coreintegrity over panels heretofore available. ang 0 3,366,718 1/1968Komada 264/45 13 Claims, 13 Drawing Figures 3,439,075 4/1969. Bauer etal. 264/45 sun/ 1 JCAN 2 SCAN .3 saw "'4 SCAN "6 Q FOR scA/v l ISEQUENCES 1 a i h E 4 2 l 0 1 SCAN ff] l 7} I T5 Ts Ts 7's RETRALE THE I7R5]: v 77951 YWEZ TIME TRET.

.. 7',- 7';- Tr Tr Tr RISE TIME BACKGROUND OF THE INVENTION The presentinvention relates generally to structural panels, and more particularlyto a novel high strength structural panel and method of making the samewhich provides a novel building construction element.

The building industry, and particularly the housing segment of thebuilding industry, has long been concerned with low-cost constructiontechniques which lend themselves to both relatively high rates ofproduction and low construction costs. The emphasis on lowcost housinghas increased as a normal result of increased population growth, theestablishment of retirement communities, and the increase in leisuretime and greater demand for second homes. Recent trends in housingconstruction have introduced the concept of mass-produced homes toeliminate many of the conventional on-site constructional techniqueswhich contribute to high building costs. The mass-produced housingconcept utilizes pre-fabricated structural components, such as walls androof sections, which are transported to the building site and assembledto form a housing unit. In order to accomplish satisfactory housingunits at relatively low cost, the prefabricated structural componentsmust be economical to manufacture, of high integrity and durability, andmust lend themselves to ease of assembly with other structuralcomponents.

Various methods have been tried in an attempt to provide panels offoamable resin material which are of a size sufficient to permitbuilding of houses therefrom and have the necessary structuralintegrity. The known techniques for producing structural panels have, inthe majority, failed to provide structural panels which have uniformcore density and are devoid of air pockets or bubbles within the corewhich tend to substantially weaken the structural panels. In oneapproach to the manufacture of structural panels, a foamable resin corematerial is introduced into a generally horizontally disposed open formor mold and allowed to rise during expansion and curing. The cured coreis than removed from the mold and cut or sliced to provide panel slabsof desired thickness. The cut core slabs are then provided withpolyester skins which are glued to the outer surfaces of the cores toprovide the finished slab. This approach is relatively costly and doesnot preclude delamination of the side skins from the core body. Thepresent invention overcomes the disadvantages in the prior art methodsof structural panel construction by providing a structural panel andmethod for making the same which results in a uniform density highstrength core integrally secured to side skin sheets, the panel Anotherobject of the present invention is to provide a novel method forproducing high strength structural panels wherein a foamed resincomposition core is disposed between fiber-reinforced side skin sheetsin a manner to effect optimum surface adhesion of the core to the skinsurfaces and thereby substantially eliminate I delamination of the sideskins from the core.

Another object of the present invention is to provide a method of makingstructural panels wherein a foamable resin composition core is formedbetween fiberreinforced side skin sheets in sandwich fashion by novelsteps which prevent the creation of pour lines and voids within the coreand thereby maximize core integrity and strength.

Another object of the present invention is to provide a high strengthstructural panel for use in building constructions and the like, whichpanel is highly durable and substantially more economical than hasheretofore been available.

Another object of the present invention is to provide a novel method ofmaking fiberreinforced side skin sheets for use with a foamable resincomposition core wherein the skins have maximum fiber surface area foradhesion to the foamable core material to prevent delamination of theskins from the core.

Another object of the present invention is to provide a novel method formaking a structural panel having a core of foamed polyurethane or thelike, wherein the method produces a core of uniform density and highintegrity independent of the size of the panel to be produced.

In carrying out the objects and advantages of the present inventionthere is provided a structural panel being particularly effective foruse in low-cost housing construction.

SUMMARY OF THE INVENTION having, in a preferred embodiment, a coresection made of a foamable resin composition such as polyurethane foam.Side skin surfaces made of fiber-reinforced polyester are disposed oneither side surface of the structural panel, each of the side skinsheets forming a side portion of a mold cavity into which the foamablecore material is introduced during manufacture of the structural panel.Each of the side skin sheets has a layer of fiber roving adjacent thecore such that the individual fibers provide increased surface area foradhesion to the foamable core material.

In manufacturing structural panels in accordance with the presentinvention, the side skins are first made and are supported with theirfiber roving surfaces in opposed parallel spaced relation. The foamableresin core composition is then introduced into the mold cavity definedbetween the side skins by means of a deposit probe. The core materialdeposit probe is caused to scan the width of the mold cavity to depositfoam at a predetermined rate, successive scans of the deposit probebeing effected at a rate to establish cross linking between successivedeposits of the foamable core material and to prevent the establishmentof voids and pour lines in the resulting panel.

Further objects and advantages of the present invention, together withthe organization and manner of operation thereof, will become apparentfrom the following detailed description of a preferred embodiment of thepresent invention when taken in conjunction with the accompanyingdrawings wherein like reference numerals designate like parts throughoutthe several views.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of amodular housing construction in accordance with the present invention;

FIG. 2 is an enlarged partial edge view taken through a structural panelin accordance with the present invention to illustrate the side skinsheets and core disposed therebetween;

FIGS. 3a-3f schematically illustrate steps in the method of making sideskin sheets for structural panels in accordance with the presentinvention;

FIG. 4 is a perspective view schematically illustrating two mold halvessecured in spaced relation to define a mold cavity for the introductionof foamable core material therebetween, a portion of the upper mold halfbeing broken away to better illustrate the core material depositingprobe;

FIGS. 5a5c schematically illustrate the steps in the method ofintroducing foamable core material between the positioned outer sideskin sheets in accordance with the present invention;

FIG. 6 graphically illustrates the manner of depositing core materialinto the mold cavity of FIG. 4 in accordance with the present invention;

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, andin particular to FIG. 1, a housing unit or structure constructed inaccordance with the present invention is indicated generally at 10. Thehousing unit 10 is constructed in accordance with what are generallytermed pre-fabricated building techniques, and includes, in theillustrated embodiment, four generally vertically disposed outer wallswhich support roof sections to define an enclosed housing unit having agenerally rectangular plan interior area. The outer walls of the housingunit 10 comprise front and rear walls, the front wall being shown at 12,and end walls, one of which is shown at 14. The roof sections areindicated at 16, there being two inclined roof sections defining a roofpeak as shown. The front wall 12 is illustrated as having a door 18providing access to the interior of the house, while the end wall 14similarly has a door 20. Any number of windows, such as shown at 22, maybe provided in the wall structural panelsas desired to accomplishsuitable natural lighting consistent with the overall size of thehousing unit constructed.

The present invention is directed to the structural panels whichcomprise the walls and roof sections of the unit 10, and the method ofmanufacturing the panels in place for subsequent transportation to abuilding site for assembly into the building unit. FIG. 2 illustrates anend view of the structural panel comprising the front wall 12 and isrepresentative of the structural panel construction in accordance withthe present invention. As there shown, the panel includes a core or mainbody portion 24 which, in the final structural panel, comprises a curedpolyurethane foam or any other suitable cured foamable resincomposition. The core 24 has side skin sheets 26 integrally secured tothe opposite side surfaces thereof. The skin sheets 26 are made offiber-reinforced polyester (FRP), commonly known as fiberglass, in amanner to present substantially more area of adhesion to the center corematerial 24 than has heretofore been practiced in structural tural panelbeing made. The mold face 28 which estab- I panels, and thussubstantially eliminates problems of side skin sheet delamination asprevalent in the prior art.

A typical structural panel in accordance with the present invention andthe method of making the same may best be understood by reference toFIGS. 3a-3f, 4 and 5a5c which sequentially illustrate the steps in themethod of making the skin sheets andthe composite structural panel. Withparticular reference to FIG. 3a, the first step in making a structuralpanel in accordance with the present invention is to form the side skinsheets which are than supported in substantially parallel spacedrelation to form a mold cavity for the introduction of foamable corematerial. A coat of polyester known as gel coat is first applied to thesurface or mold face 28 of a mold, indicated generally at 30, having aplan area substantially equal to the area of the struclishes the outerconfiguration of the finished panel may have a surface pattern thereinsimulating drop-siding, wood shingles, or plaster. The gel coat isuniformly applied onto the mold surface 28 through a suitable spraynozzle 32 to provide a uniform layer or thickness of gel coat ofapproximately 0.015 inch thickness. The first layer of gel coat servesto give a satin texture to the finished skin sheet. After the gelcoating has been applied, a layer of polyester resin is depositeddirectly onto the gel coat layer, as indicated in FIG. 3b, through aspray nozzle 34 to provide a resin layer of uniform thickness. Next, alayer of chopped glass strands or glass roving 36 is applied to thefirst layer of resin before it cures through suitable means such as adischarge nozzle 38 as shown in FIG. 3c. After depositing the glassroving onto the first layer of polyester resin, the fibers are forcedinto the first layer of resin by suitable means such as a roller device40 to insure that the fibers become completely impregnated with thepolyester resin and to provide the reinforcing characteristics of thelaminate. Rolling the fiber strands into the polyester resin coatingalso serves to force all air out of the composite laminate and preventthe creation of potential weak spots in the skin sheet.

After the first layer of chopped glass roving has been forced into thefirst layer of polyester resin, a second layer of polyester resin isapplied onto the resin-fiber laminate through the spray nozzle 34 asshown in FIG. 3e, the second layer of polyester resin being appliedbefore curing of the first layer so as to insure cross-linking betweenthe first and second layers of resin. Thereafter,

a second layer of chopped fiberglass roving 42 is applied to the secondlayer of resin by the discharge nozzle 38 prior to curing of the secondresin layer. The second layer of glass fibers 42 is not, however, rolledor otherwise forced into the second layer of resin. Rather, fiber endportions of the second layer of fibers 42 are allowed to partiallyproject outwardly from the second layer of resin, but with each of thefibers being at least partially integrally embedded into the secondlayer of resin. The resin and fiberglass roving layer are then allowedto cure. In this fashion, the ends of the individual fibers 42projecting outwardly from the second layer of resin will providesubstantially greater adhesion area for the foamed core to be associatedtherewith as will become more apparent hereinbelow.

As noted, two skin sheets 26 comprise the inner and outer surfaces ofeach of the structural panels such as indicated at 12 in FIG. '2. Aftermaking two skin sheets in accordance with the method above-described,two molds 30 with skin sheets 26 therein are supported in parallelspaced relation with the outwardly projecting fibers 42 in opposedrelation as shown schematically in FIG. 4. The two molds 30 aremaintained in spaced relation by closure spacers 44 provided along threemarginal edge portions of the rectangularly shaped molds 30 to leave anopening 46 across one edge portion providing access to the mold cavitydefined between the spaced molds. While the molds 30 are hereinillustrated and described as being rectangular in plan configuration, itwill be appreciated that the molds may be of substantially any desiredplan configuration with the mold cavity defined therebetween beingclosed by suitable spacer means except along one edge portion of themold assembly, preferably along a major dimension of the mold cavity.The mold halves 30 and the associated spacers 44 may be secured togetherthrough any suitable means whichallow release of the mold halves 30 andremoval of the spacers 44 upon completion of a structural panel.Suitable means (not shown) are employed to reinforce the mold sectionswhen in assembled relation so that the mold sections will not bow orotherwise deform during curing of the core material which may createpressures against the mold sections approaching 1,000 p.s.ft.

With the mold halves 30 and their associated skin sheets 26 secured inspaced relation, a core material deposit means comprising an elongatedtubular material depositing probe 48 is inserted into the opening 46such that the discharge end of the probe 48 is disposed adjacent thefurthest portion of the cavity from the opening 46. For example, with arectangular mold cavity as illustrated in FIG. 4, the elongated probe 48is inserted such that its discharge end is adjacent either of the farcorners of the mold cavity. Prior to depositing the foamable corematerial into the mold cavity between the spaced skin sheets, tubularconduits for electrical wiring or plumbing systems may be inserted intothe cavity and suitably retained in fixed relation position therein forsubsequent use in the housing unit constructed with the structuralpanels inaccordance with the present invention.

The core material discharge probe 48 is connected to a conventionalsource of polyurethane foam (not shown) which is selectively operable tointroduce a foamable resin composition into the elongated probe 48 andeffect discharge thereof from the outer end of the probe in accordancewith predetermined rates of deposit. Upon inserting the elongated probe48 into the mold cavity between the spaced skin sheets as shown in FIG.4, the foamable resin composition is discharged from the probe 48 intothe mold cavity and the probe is caused to move in a scanning directionacross the mold cavity generally transverse to the longitudinal axis ofthe discharge probe 48. The foamable resin composition is deposited intothe mold cavity at a predetermined rate which is a function of the flowpassage size in the probe 48 and the rate at which the probe is causedto scan or move across the mold cavity, considered in the scandirection. With reference to FIG. 5a, the discharge probe 48 is causedto move in a direction indicated by arrow 50 from the left-hand edge ofthe mold cavity to the righthand edge thereof leaving a uniform depositof resinous core material 24 deposited within the mold cavity asindicated in FIG. 5b.

When the discharge probe 48 reaches the opposite edge of the mold cavityfrom which it initially began,

it is selectively retracted in an axial direction outwardly from thebottom of the mold cavity and returned in a retrace direction to theleft-hand edge of the mold cavity preparatory to a subsequent scan.During the retrace movement of the probe 48, the supply of resinous corematerial to the probe is shut off so as not to be introduced into themold cavity. The rate of movement of the deposit probe during retracingto its initial starting position following a deposit scan movement isestablishedsuch that the previous deposit of foamable resin corecomposition will have reached a predetermined rise but will not havecured, thus insuring that the next layer of foamable core material to bedeposited will cross-link with the prior resin deposit. The rise of eachsuccessive deposit of resinous core material is allowed to substantiallyreach its maximum limit before applying another layer to preventcontinued expansion of the prior deposit which might create excessivecompaction of the deposited core material and excessive pressure againstthe skin sheets (at the strain point which occurs after the rise time,or expansion, is terminated and at which time the material is still hotand sufficiently soft to effect the desired cross-linking). It isimportant that each scan or deposit of the foamable core material bemade prior to curing of the previous deposit so that integralcross-linking is effected between successive deposits, and pour linesare prevented which would substantially reduce core integrity and weakenthe structural strength of the resulting panel.

FIG. 5c schematically illustrates a plurality of scan passes of thedeposit probe 48 to establish successive deposits 24, 24a, 24b, 24c, 24dand 24e, each successive scan or deposit of foamable core material beingeffected prior to curing of the next preceding deposit. It is importantthat the amount of material discharged from the deposit probe,considered in pounds per minute, and the rate at which the probe ismoved during its scanning movement, considered in feet per minute, be

selected to effect cross-linking between successive deposits of thefoamable core material. In accordance with the present invention, thedeposit of the foamable core material is effected in a manner to obtaina core 24 between the skin sheets 26 of uniform density and highintegrity independent upon the size of the structural panel beingproduced. The scan rate and the deposit delivery rate may vary dependingupon the density of the foamable core material employed. After pouringthe last scan deposit of foamable core material,

a plate (not shown) or other suitable means is secured on the upper openedge of the mold cavity to close the same so that the core material isallowed to expand against the plate to effect an even edge surface ofthe core with the associated skin sheets.

It has been found that using a two pound foam at a deposit rate and scanrate such that the expanded foamablecore material will rise to a heightof about 2 feet, considered with the mold cavity generally verticallydisposed, or will expand about 2 feet in a horizontal direction,considered with the mold cavity in a generally horizontal position asindicated in FIGS. 4 and Sa-Sc, will result in a satisfactory panel coreof high integrity. Introduction of the foamable core material at Y ahigher rate tends to cause excessive pressures within the mold cavityresulting in compactions and undesirable air entrapments resulting invoids which are detrimental to the integrity of the resulting structuralpanel. On the other hand, introducing the foamable core material atlower rates reduces the efficiency with which the structural panels maybe produced and increases the number of scans necessary to accomplishfilling of the mold cavity.

It has been found that a delivery rate for the foamable core material inaccordance with the relationship Mr=htSD/Tr%Tret provides a highlydesirable core integrity; where t is the thickness of the cavity to befilled, S is the length of a scan or the length of the cavity, D is thedensity of the chosen foamable core material after expansion, Tr is therise time for the particular foam material selected, Tret is the timerequired to retract the probe and retrace it to its starting edge of thecavity, and h is the desired height of expansion of the particulardeposit of foamable core material which is preferably selected to equal2 feet. With a material deposit rate in accordance with the foregoingequation, the scan rate (Sr) or speed at which the probe should becaused to traverse across the width of the mold cavity is selected inaccordance with the equation Sr=S/TrTret. FIG. 6 graphically illustratesthe various parameters comprising the above equations for core materialdelivery rate and deposit probe scan rate, where T represents the timerequired for one scan of the deposit probe.

In accordance with one example of the present invention, a mold cavityhaving a 2 %-inch thickness,

a 12-foot depth, and a 24-foot width was filled with a foamable corematerial (such' as a polyurethane of the type commercially availablefrom M & R Plastics,

St. Louis, Miss. under the tradename Mistafoam and identified bymanufacturers Ser. Nos; 85 2-S/801 H; having a rise time (Tr) of 190seconds. With the probe retrace time (Tr'et) being selected at 15seconds, the delivery rate in accordance with the above equation wouldbe approximately about 7.5 pounds per minute. The foam materialdepositing equipment should than be adjusted to supply material at thisrate, and the probe scan rate (Sr) determined in accordance with theabove equation would be approximately 8.2 feet per minute, the timerequired to fill the mold cavity having the aforenoted dimensionalconfiguration being approximately 17.6 minutes. If a larger mold cavityis selected, it would be necessary to increase the transverse scan speedof the probe and to vary the core material delivery rate as defined bythe equation Mr=ht SD/Tr-Tret. The foamable core material would in suchcircumstances be again deposited during a scanning movement at aconstant material delivery rate in accordance with the abovev notedequation Mr htSD/Tr Tm,

and the rate of scan of the injection means would be in accordance withthe above noted equation Sr=S/Tr-Tret. For example, if the size of themold cavity were increased in thickness, i.e., the distance between thespaced skin sheets in the molds 30, the delivery rate would be increasedby either employing a single deposit probe having a greater corematerial delivery rate, or employing deposit means comprising aplurality of deposit probes to introduce the required additional corematerial in essentially the same period of time as given for the aboveexample. In any event,

the deposit rate should be limited so as not to result in an expandedfoam depth of greater than 2 feet per scan of the deposit probe.

It has been found that the method of introducing the foamable corematerial as above described results in elimination of pour lines andsubstantially increases the adhesive characteristics of the corematerial to the skin sheets whereby to prevent delamination of the corematerial from the skin sheets after the completed structural panel isremoved from the mold 30. It has also been found that structural panelsmade in accordance with the aforedescribed method provide substantialeconomic advances over the methods heretofore employed through maximumutilization of the machinery associated with the deposit probes toeffect core material deposit and scanning of the probes.

In addition to the high integrity offered by the structural panels inaccordance with the present invention, cracking and warping of thepanels is resisted. Additionally, the structural panels are imperviousto termites, rodents, fungi, acid and other pollutants. Exterior colorsfor the structural panels may be impregnated into the skin sheetsthereby eliminating the need for continued maintenance, althoughpainting of the panels may be readily accomplished if desired. It hasbeen found that housing constructions employing the structural panels inaccordance with the present invention provide substantial economicsavings over conventional housing constructions thereby making thedescribed modular housing units particularly desirable for low-costhousing with a minimum of maintenance expense.

While a preferred embodiment of a structural panel in accordance withthe present invention, and a preferred method of making the structuralpanels, have been illustrated and described, it will be understood thatchanges and modifications may be made therein without departing from theinvention in its broader aspects.

We claim:

1. A method of making a structural panel comprised of fiber-reinforcedskin sheets having a thermosetting foamable resin composition coretherebetween for use in building structures and the like, comprising thesteps of applying a first layer of gel coat to spaced surfaces of a moldwhich are configured to provide a panellike structure applying a firstlayer of polyester resin onto said gel coat, applying a first layer ofglass fiber roving onto said layer of polyester resin before curingthereof, forcing the glass fiber roving into said first layer of resinin a manner to impregnate the roving fibers into said tion into a cavitydefined by said spaced surfaces such that the thermosetting corecomposition substantially fills said cavity and integrally adheres tosaid opposing spaced surfaces and outwardly projecting fibers thereon toprovide an increased area of surface adhesion between the thermosettingcore composition and each of said skin sheet fibers, and effectingcuring of said thermosetting core composition.

2. The method of claim 1 wherein said thermosetting foamable corecomposition is introduced into said cavity through deposit meansinserted through an access opening into said cavity.

3. The method of claim 2 wherein said deposit means comprises anelongated deposit probe having a length sufficient to introduce thethermosetting foamable core material into the most distant area of saidcavity from said opening therein, and including the step of moving saidprobe in a direction transverse to the direction of insert of thedeposit probe to deposit core material into said mold at a predeterminedrate.

4. The method of claim 3 wherein said deposit probe is movedtransversely in successive scans to successively depositsaidthermosetting foamable core material into said cavity at a rate ofdeposit such that each successive deposit is applied to the nextpreceding deposit prior to curing of said next preceding deposit to forman integral core upon curing thereof.

5. The method of claim 1 including the step of inserting tubularconduits into said cavity in predetermined positions therein prior tointroducing said thermosetting foamable core material into said cavity.

6. A method of making a structural panel comprising the steps ofsupporting a pair of fiber-reinforced generally rigid skin sheets ofsubstantially identical configuration in spaced relation, closing themarginal edge spaces between said spaced skin sheets along all but oneedge portion thereof to define a closed cavity between said skin sheetsexcept for said open edge portion, inserting deposit means through saidopen edge, introducing into said cavity a thermosetting foamable resincore composition through said deposit means, said deposit means beinginitially positioned to deposit said thermosetting foamable corematerial into the portion of the cavity furthest removed from saidopening at a measured rate, said deposit means being thereafter moved ina direction generally transversely to the direction of entry of saiddeposit means into the cavity to scan the same, said scanning movementof the deposit means being continuously repeated to deposit saidthermosetting foamable core material into said cavity to substantiallyfill the same, each successive scanning movement of the deposit meansbeing effected to deposit a measured quantity of foamable core materialonto the preceding deposit prior to curing of said preceding deposit,and curing the deposited thermosetting foamable core material withinsaid cavity to form an integral core connected to said skin sheets.

7. The method as defined in claim 6 wherein each of said skin sheets ismade of fiber-reinforced polyester having a plurality of fibersprojecting outwardly from the inner surface thereof for engagement withsaid foamable core material for adhesive connection thereto.

8. The method as defined in claim 6 wherein said deposit means includesan elongated core material depositing probe, and wherein successivescans of the probe are effected after measured incremental axialwithdrawal of the probe following each scan movement.

9. The method of claim 6 including the step of inserting tubularconduits into said cavity prior to introducing the foamable corematerial therein.

10. The method of making a structural panel having side skin sheets anda core integrally sandwiched therebetween, comprising the steps ofsupporting a pair of side skin sheets in spaced relation to define amold cav- Mr ht SD/Tr Tre t,

and effecting the rate of scan of said deposit means in accordance withthe equation Sr S/Tr-Tret,'

where Mr is the core material delivery rate measured in pounds perminute,.h is the height in feet of rise of the expanded thermosettingfoamable core material, I is the thickness of the cavity measured infeet, considered in a direction between the side skin surfaces, S is thelength in feet of scan movement of the material depositing means or thewidth of the mold cavity, D is the density of the chosen thermosettingfoamable core material after expansion and curing, Tr is the rise timein minutes for the selected thermosetting foamable core material, Tretis the time in minutes required to withdraw the depositing means for thenext successive scan of the deposit means, and Sr is the'rate in feetper minute of scan of the deposit means.

11. A method of making a structural panel including fiber-reinforcedskin sheets that engage with a thermosetting foamable core compositionfor use in building structures and the like, comprising the steps ofapplying a first layer of gel coat to each of a pair of mold surfaceshaving a configuration conforming to the desired outer configuration ofthe panel desired, applying a first layer of polyester resin onto saidgel coats, applying a first layer of glass fiber roving onto said layersof polyester resin before curing thereof, forcing the glass fiber rovinginto each of said first layers of resin in a manner to impregnate theglass roving fibers into each of said first layers of resin, applying asecond layer of polyester resin into the combined first layers of resinand fibers, applying a second layer of glass fibers onto each of saidsecond layers of resin without forcing and before said second layers ofresin are cured such that portions of thefibers of each of said secondlayers of.

fibers project outwardly from each of said second layers of resin toprovide fiberreinforced side skin sheets having fibers projectingoutwardly from the surfaces thereof, supporting the resulting pair ofpanel-like configuration fiber-reinforced side skin sheets in spacedrelation to define a mold cavity having a thickness substantially equalto the thickness of the desired panel, closing said cavity along themarginal edge portions thereof except for an opening extending along onemarginal edge portion to provide access to the interior of the moldcavity, each of said skin sheets having the outwardly projecting fibersof said second layers projecting outwardly from the surface thereofopposing the other spaced skin sheet, introducing a thermosettingfoamable core composition into said cavity such that the thermosettingcore composition substantially fills said cavity and integrally adheresto said opposing skin sheets and outwardly projecting fibers to providea greater adhesion area between the core composition and each of saidskin sheet fibers, and effecting curing of said core composition.

12. The method of claim 11 wherein a deposit means comprising anelongated deposit probe is inserted into said cavity through an accessopening and has a length sufficient to introduce the thermosettingfoamable core material into the most distant area of said cavity fromsaid opening therein, and including the step of moving said probe in adirection across the width of the mold in successive scans tosuccessively deposit said thermosetting foamable core material into saidcavity at a rate of deposit such that each successive deposit is appliedto the next preceding deposit prior to curing of said next precedingdeposit to form an integral core upon curing thereof.

13. A method of making a structural panel for use in building structuresand the like, comprising the steps of I supporting a pair offiber-reinforced side skin sheetsin spaced relation to define a moldcavity having a plan configuration and thickness substantially equal tothe shape of the panel desired, closing said cavity along the marginaledge portions thereof except for an opening extending along one marginaledge portion to provide access to the interior of the mold cavity, eachof said side skin sheets including a cured body of a panel-likeconfiguration having a plurality of fibers projecting outwardly from thesurface thereof opposing the other spaced skin sheet, inserting adeposit means into said cavity and moving said deposit means generallytransversely to the direction of insertion to introduce a thermosettingfoamable composition along a line of deposit into said cavity andwithdrawing said deposit means after each successive transverse scan,each successive transverse scan being performed prior to curing of thethermosetting foamable composition previously deposited, such that thethermosetting foamable composition substantially fills said cavity andintegrally adheres to said opposing skin sheets and outwardly projectingfibers to provide a greater adhesion area between the thermosettingfoamable composition and each of said skin sheet fibers, and effectingcuring of said thermosetting foamable composition.

1. A method of making a structural panel comprised of fiberreinforcedskin sheets having a thermosetting foamable resin composition coretherebetween for use in building structures and the like, comprising thesteps of applying a first layer of gel coat to spaced surfaces of a moldwhich are configured to provide a panellike structure applying a firstlayer of polyester resin onto said gel coat, applying a first layer ofglass fiber rovinG onto said layer of polyester resin before curingthereof, forcing the glass fiber roving into said first layer of resinin a manner to impregnate the roving fibers into said first layer ofresin, applying a second layer of polyester resin into the combinedfirst layer of resin and fibers, applying a second layer of glass fibersonto said second layer of resin before said second layer of resin iscured such that portions of the fibers of said second layer of fibersproject outwardly from said second layer of resin on said spacesurfaces, curing said layers of resin, and introducing a thermosettingfoamable core composition into a cavity defined by said spaced surfacessuch that the thermosetting core composition substantially fills saidcavity and integrally adheres to said opposing spaced surfaces andoutwardly projecting fibers thereon to provide an increased area ofsurface adhesion between the thermosetting core composition and each ofsaid skin sheet fibers, and effecting curing of said thermosetting corecomposition.
 2. The method of claim 1 wherein said thermosettingfoamable core composition is introduced into said cavity through depositmeans inserted through an access opening into said cavity.
 3. The methodof claim 2 wherein said deposit means comprises an elongated depositprobe having a length sufficient to introduce the thermosetting foamablecore material into the most distant area of said cavity from saidopening therein, and including the step of moving said probe in adirection transverse to the direction of insert of the deposit probe todeposit core material into said mold at a predetermined rate.
 4. Themethod of claim 3 wherein said deposit probe is moved transversely insuccessive scans to successively deposit said thermosetting foamablecore material into said cavity at a rate of deposit such that eachsuccessive deposit is applied to the next preceding deposit prior tocuring of said next preceding deposit to form an integral core uponcuring thereof.
 5. The method of claim 1 including the step of insertingtubular conduits into said cavity in predetermined positions thereinprior to introducing said thermosetting foamable core material into saidcavity.
 6. A method of making a structural panel comprising the steps ofsupporting a pair of fiber-reinforced generally rigid skin sheets ofsubstantially identical configuration in spaced relation, closing themarginal edge spaces between said spaced skin sheets along all but oneedge portion thereof to define a closed cavity between said skin sheetsexcept for said open edge portion, inserting deposit means through saidopen edge, introducing into said cavity a thermosetting foamable resincore composition through said deposit means, said deposit means beinginitially positioned to deposit said thermosetting foamable corematerial into the portion of the cavity furthest removed from saidopening at a measured rate, said deposit means being thereafter moved ina direction generally transversely to the direction of entry of saiddeposit means into the cavity to scan the same, said scanning movementof the deposit means being continuously repeated to deposit saidthermosetting foamable core material into said cavity to substantiallyfill the same, each successive scanning movement of the deposit meansbeing effected to deposit a measured quantity of foamable core materialonto the preceding deposit prior to curing of said preceding deposit,and curing the deposited thermosetting foamable core material withinsaid cavity to form an integral core connected to said skin sheets. 7.The method as defined in claim 6 wherein each of said skin sheets ismade of fiber-reinforced polyester having a plurality of fibersprojecting outwardly from the inner surface thereof for engagement withsaid foamable core material for adhesive connection thereto.
 8. Themethod as defined in claim 6 wherein said deposit means includes anelongated core material depositing probe, and wherein successive scansof tHe probe are effected after measured incremental axial withdrawal ofthe probe following each scan movement.
 9. The method of claim 6including the step of inserting tubular conduits into said cavity priorto introducing the foamable core material therein.
 10. The method ofmaking a structural panel having side skin sheets and a core integrallysandwiched therebetween, comprising the steps of supporting a pair ofside skin sheets in spaced relation to define a mold cavitytherebetween, closing the mold cavity along at least three marginal sideedges thereof by spacer means, inserting deposit means into said moldcavity for depositing a thermosetting foamable core material into themold cavity, moving the deposit means in a scan direction across thewidth of the cavity while depositing core material, and effecting thedeposit of said thermosetting foamable core material during saidscanning movement of said deposit means at a constant material deliveryrate in accordance with the equation Mr ht SD/Tr- Tret, and effectingthe rate of scan of said deposit means in accordance with the equationSr S/Tr-Tret; where Mr is the core material delivery rate measured inpounds per minute, h is the height in feet of rise of the expandedthermosetting foamable core material, t is the thickness of the cavitymeasured in feet, considered in a direction between the side skinsurfaces, S is the length in feet of scan movement of the materialdepositing means or the width of the mold cavity, D is the density ofthe chosen thermosetting foamable core material after expansion andcuring, Tr is the rise time in minutes for the selected thermosettingfoamable core material, Tret is the time in minutes required to withdrawthe depositing means for the next successive scan of the deposit means,and Sr is the rate in feet per minute of scan of the deposit means. 11.A method of making a structural panel including fiber-reinforced skinsheets that engage with a thermosetting foamable core composition foruse in building structures and the like, comprising the steps ofapplying a first layer of gel coat to each of a pair of mold surfaceshaving a configuration conforming to the desired outer configuration ofthe panel desired, applying a first layer of polyester resin onto saidgel coats, applying a first layer of glass fiber roving onto said layersof polyester resin before curing thereof, forcing the glass fiber rovinginto each of said first layers of resin in a manner to impregnate theglass roving fibers into each of said first layers of resin, applying asecond layer of polyester resin into the combined first layers of resinand fibers, applying a second layer of glass fibers onto each of saidsecond layers of resin without forcing and before said second layers ofresin are cured such that portions of the fibers of each of said secondlayers of fibers project outwardly from each of said second layers ofresin to provide fiberreinforced side skin sheets having fibersprojecting outwardly from the surfaces thereof, supporting the resultingpair of panel-like configuration fiber-reinforced side skin sheets inspaced relation to define a mold cavity having a thickness substantiallyequal to the thickness of the desired panel, closing said cavity alongthe marginal edge portions thereof except for an opening extending alongone marginal edge portion to provide access to the interior of the moldcavity, each of said skin sheets having the outwardly projecting fibersof said second layers projecting outwardly from the surface thereofopposing the other spaced skin sheet, introducing a thermosettingfoamable core composition into said cavity such that the thermosettingcore composition substantially fills said cavity and integrally adheresto said opposing skin sheets and outwardly projecting fibers to providea greater adhesion area between the core composition and each of saidsKin sheet fibers, and effecting curing of said core composition. 12.The method of claim 11 wherein a deposit means comprising an elongateddeposit probe is inserted into said cavity through an access opening andhas a length sufficient to introduce the thermosetting foamable corematerial into the most distant area of said cavity from said openingtherein, and including the step of moving said probe in a directionacross the width of the mold in successive scans to successively depositsaid thermosetting foamable core material into said cavity at a rate ofdeposit such that each successive deposit is applied to the nextpreceding deposit prior to curing of said next preceding deposit to forman integral core upon curing thereof.
 13. A method of making astructural panel for use in building structures and the like, comprisingthe steps of supporting a pair of fiber-reinforced side skin sheets inspaced relation to define a mold cavity having a plan configuration andthickness substantially equal to the shape of the panel desired, closingsaid cavity along the marginal edge portions thereof except for anopening extending along one marginal edge portion to provide access tothe interior of the mold cavity, each of said side skin sheets includinga cured body of a panel-like configuration having a plurality of fibersprojecting outwardly from the surface thereof opposing the other spacedskin sheet, inserting a deposit means into said cavity and moving saiddeposit means generally transversely to the direction of insertion tointroduce a thermosetting foamable composition along a line of depositinto said cavity and withdrawing said deposit means after eachsuccessive transverse scan, each successive transverse scan beingperformed prior to curing of the thermosetting foamable compositionpreviously deposited, such that the thermosetting foamable compositionsubstantially fills said cavity and integrally adheres to said opposingskin sheets and outwardly projecting fibers to provide a greateradhesion area between the thermosetting foamable composition and each ofsaid skin sheet fibers, and effecting curing of said thermosettingfoamable composition.